Not Applicable
This invention has particular application to the replacement of flexible bearing supports of a type used in Westinghouse Electric Company steam turbines from the late 1940s to the mid 1960s, but its utility is not confined thereto. Such turbines and their associated generators are massive, and expensive, and interruption of their use is of grave importance. They usually have two units, a high pressure turbine and a low pressure turbine, connected, with bearings in which aligned shafts of the two turbines are journalled. The bearings are supported by flexible plates, which, after some length of time, have been liable to break leaving the bearings unsupported, resulting in damage to the bearings and the turbines themselves. For reference, in this type of steam turbine, the bearing design is typically steel backed, babbitt lined, oil film lubricated, and not of rolling element design.
In this type of bearing support pairs of flexible support plates, one on either side of the shaft being supported, are connected at their upper ends to arms of a yoke extending transversely of the shaft. The yoke is symmetrical, and the support plate assemblies are mirror images of one another. In prior art assemblies the flexible support plates extend between a floor plate and an upper block, the floor plate being mounted on a sole plate, which is in turn mounted onto a foundation. The upper block is connected to the bearing-supporting yoke. The flexible support plates, sometimes referred to hereinafter as flex plates, are rectangular, with flat, parallel sides, and at their top and bottom edges, fit into channels in the top block and floor plates. The channels have chamfered sides, and the flexible support plates are welded along their opposite sides in the channels. Over a period of years, a combination of static stresses and a large number of cyclic stresses causes the flexible support plates to break at or near the joint with the pedestal base. When either the bottom joint or the top block joint fails, the bearing function is lost and there is much damage to the turbine.
An object of this invention is to provide a bearing spring plate pedestal that obviates the problem of breakage. As has been pointed out, it has particular application to the replacement of bearing supports that have failed or are likely to fail, and to the method of their replacement, although its utility is not confined thereto.
In accordance with this invention, generally stated, a bearing spring plate pedestal is provided which comprises a flexible plate integral, that is, of one piece, with top and bottom mounting blocks, the flexible plate and mounting blocks meeting at large radii, polished and substantially free from stress risers. The terms xe2x80x9cradiusxe2x80x9d and xe2x80x9cradiixe2x80x9d as applied to the invention, are used herein to include any arcuate transition area with a smooth, continuous curve spanning 90 degrees from the flexible plate to a top or bottom block, not just a circular cylindrical arc. The flexible plate and top and bottom block are made from a continuous forging of alloy steel, heat treated. Preferably, a tapered shim is positioned between a top mounting block and the bearing-supporting yoke to permit accommodation for tilting of the bearing. In the illustrative embodiment shown and described, two pairs of sets of bearing plates are shown, supporting shafts journalled in bearings supporting aligned and connected shafts of a high pressure turbine and a low pressure turbine. The bearing plates of each set are mirror images of one another, and except as noted, the two bearing supports illustrated are mirror images of one another. Single bearings are supported with the same apparatus, and the description of one of the flexible plates of this invention and its installation is equally as applicable to the single pair of a set of mirror image supports of a single bearing as to the mirror image supports of the two bearing arrangement of the preferred embodiments.
In the method of replacing a failed bearing flexible support plate, there are three preferred methods. In the first, any protruding part of the failed plate is machined, as by milling or grinding off with a portable milling machine or grinder, both methods being encompassed by the term xe2x80x9cmachinedxe2x80x9d as used herein, and that part and the top surface of the pedestal base surrounding it are machined so that they are flat, and this top surface now becomes the mating surface to the replacement flexible pedestal support.
A drill fixture, with holes in exact correspondence with holes in the bottom block is positioned over the exposed surface of the pedestal base in precisely the position to be assumed by the pairs of flexible plates, holes are drilled in the pedestal base in conformance with a hole pattern in the drill fixture that corresponds exactly with a hole pattern in the bottom block, and tapped. A common method of making the holes in a drill fixture is to make the diameters of the holes to be the diameters of the tap drills to be used to make the holes in the pedestal base, and not the diameters of the clearance holes of the bottom block of the bearing spring plate pedestal to be installed. If epoxy is used to help secure the bottom block of the flexible plate to the pedestal base and to fill any voids that might be found under the bottom block, it is applied before the hold-down bolts are torqued down, and then the bolts are tightened.
In a second method, any protruding broken flexible plate is machined down so that they protrude a short distance, as, for example, approximately xc2xc inch, but are not completely eliminated. The surface area around the protruding broken flexible plate or plates, is machined flat, preferably leaving a narrow strip, for example, about xc2xcthe of an inch per side, of unmachined surface around the protruding flexible plate stub or stubs, contiguous the protruding flex plate stub. A groove sufficiently deep to accommodate the protruding broken flexible plate stub, and wide enough to bridge the distance beyond the unmachined strips is machined into the bottom surface of the lower block A similar groove is machined into the undersurface of each plate of the drill fixture. Epoxy can be used to form a permanent chock in the gaps around the remains of the protruding flexible plates, and any other gaps between the bottoms of each of the flexible support structures and the tops of the mating sections of the pedestal base. The use of the drill fixture is common to all the methods in the preferred embodiments.
The third method, is to grind the broken and protruding remains of the original flexible plates, and to leave them protruding for a short distance, as, for example, xc2xc of an inch, and not to machine the base plate flat. The drill fixture, with grooves in the bottom, is used as in the prior two methods, but the two sides of the drill fixture are not expected to sit flatly on the top surfaces of the pedestal base. The fixture is fastened by a block or shim or otherwise so that it remains properly located with enough rigidity to function properly. The drill fixture as in the other two cases is used to locate and drill the hold-down bolt holes. In this method, shims or small jack bolts are expected to be required to level and hold in position the replacement flexible support structures. In this case, epoxy is used to form a permanent chock in the gaps around the remains of the protruding flex plates and other gaps between the bottom of each of the flexible support structures and the top of the mating section of the pedestal base. Once the flexible support structures are properly bolted in place and the epoxy is suitably cured, then the assembly of the remainder of the bearing support structure, bearing and turbine rotor is as first described above.
Preferably, at least the rotor of the turbine the bearing support for which is being replaced is removed and the old pedestal equipment is removed, leaving the broken surface of the flexible support plate or plates exposed, so that the projecting part of the broken flexible plate and an area around it can be machined. Of course, both rotors can be removed, but it has been found sufficient to remove only the one turbine rotor. After the parts are machined, the new flexible supports are set in place. Trial shim plates are installed, the yoke is installed, and the lower half of the bearing is installed. A stub shaft is mounted on the end of the remaining turbine rotor coupling hub, so as to duplicate approximately where the journal for the bearing adjacent the turbine will be located when the removed turbine shaft is repositioned. The upper half of the bearing and the bearing cover are installed. The bearing yoke can be moved around so that the bearing is aligned to the stub shaft. When aligned, the bearing and yoke will be in almost identical positions to that which will be required when the normal turbine rotor is installed. The hold down bolts are now positioned and tightened to hold the flexible supports in place, and shim plates made and installed to obtain the proper tilt to minimize flexing of the flexible support plates. If it is desired to install the pedestal with epoxy to secure the support flexible pedestals to the pedestal base, this can be done at the time the bolts are put in.
After the hold down bolts are installed completely and alignment is verified, then the bearing cover, bearing upper half and stub shaft are removed. Holes through the top block are provided so that an extension rod and proper tool can be used to torque certain bolts through the bottom block that are otherwise hard to torque to the specified values. If epoxy has been used, after the epoxy has hardened, the shim plates, yoke and bearing lower half can be installed. The bearing pedestal and bearing are now ready for installing the removed turbine rotor.